1.5 Casting and Ranges of Variables

What is casting?

Casting explicitly converts a value from one data type to another. Widening (int → double) happens automatically and loses no data. Narrowing (double → int) requires an explicit cast like `(int) x` and can lose information, since Java simply truncates (drops) the decimal part rather than rounding.

Integer division vs. casting

Dividing two ints performs integer division, truncating any remainder (7/2 = 3). To get a decimal result, cast at least one operand to double before dividing, e.g., `(double) 7 / 2` = 3.5. Casting the whole expression after division won't help — the truncation already happened.

Ranges of variables

Primitive types have fixed storage sizes and value ranges. An int holds whole numbers roughly ±2.1 billion (32-bit). A double stores decimal values with much greater range and precision. Assigning a value outside a type's range, or improperly narrowing, causes overflow or data loss.

Key terms

Casting

Explicitly converting a value from one data type to another, e.g., (int) 5.7.

Widening cast

Automatic conversion to a larger type (e.g., int to double) with no data loss.

Narrowing cast

Explicit conversion to a smaller type (e.g., double to int) that can lose data through truncation.

Integer division

Division of two ints that truncates any decimal remainder, e.g., 7/2 = 3.

How to force decimal division

Cast at least one operand to double before dividing, e.g., (double) a / b.

Try an AP-style question

What is (int) 3.99?

1. 4
2. 3.99
3. 3.0
4. 3